1. The Field of the Invention
This invention relates to lifting devices and, more particularly, to novel systems and methods related to live-line cranes.
2. The Background Art
Live-line lifting devices are machines capable of dispensing and retracting a length of line. Such devices are typically used to manipulate objects too massive to safely manipulate manually. Many current live-line lifting devices employ a winch that winds and unwinds a cable. These winches are typically driven by electric or hydraulic motors. Accordingly, they have certain disadvantages.
For example, spooling winches are typically expensive. They occupy a significant amount of space. They require stops to prevent the cable from being wrapped all the way on or off the spool. Moreover, spooling winches decrease in lifting capacity as the cable is wound onto the spool. That is, the winch produces a constant torque, but the moment arm acting against the winch increases as cable wraps around the spool and increases its diameter. Accordingly, current winch devices may begin lifting a heavy object, but fail or stall once the object has been lifted to a certain point. This increase in diameter also causes an increase in the speed at which cable is retracted, even while the winch operates at a constant rotational velocity
Accordingly, what is need is a live-line lifting device that is compact and inexpensive to manufacture. Additionally, the device should dispense and retract line at a constant rate when desired. Moreover, the device should support the same maximum load at full retraction of the line that it can at full extension of the line.